brew.sh: enforce HOMEBREW_FORCE_BREW_WRAPPER more strictly
#20400
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`HOMEBREW_FORCE_BREW_WRAPPER` can be used as a security/compliance feature, but allowing it to be disabled by setting `HOMEBREW_NO_FORCE_BREW_WRAPPER` leaves a pretty large hole in it that allows it to be sidestepped. Let's fix that by actually checking the path of the process that called `brew`, and the verify that that path matches the configured value of `HOMEBREW_NO_FORCE_BREW_WRAPPER`.
MikeMcQuaid
reviewed
Aug 11, 2025
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| HOMEBREW_BREW_WRAPPER: { | ||
| description: "If set, use wrapper to call `brew` rather than auto-detecting it.", | ||
| }, |
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We need to go through a deprecation cycle before dropping this.
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| HOMEBREW_NO_FORCE_BREW_WRAPPER: { | ||
| description: "If set, disables `$HOMEBREW_FORCE_BREW_WRAPPER` behaviour, even if set.", | ||
| boolean: true, | ||
| }, |
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Same here.
Could add something HOMEBREW_DISABLE_NO_FORCE_BREW_WRAPPER if you want the ability to disable this functionality.
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| require "fiddle" | ||
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| libproc = Fiddle.dlopen("/usr/lib/libproc.dylib") |
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What if this file doesn't exist?
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It actually won't; it lives in the dyld cache. But, I suppose you were asking what happens if it fails. It exits immediately with an error like:
❯ ./test.rb
/Users/carlocab/.rbenv/versions/3.4.5/lib/ruby/3.4.0/fiddle.rb:93:in 'Fiddle::Handle#initialize': dlopen(/path/to/nonexistent.dylib, 0x0009): tried: '/path/to/nonexistent.dylib' (no such file), '/System/Volumes/Preboot/Cryptexes/OS/path/to/nonexistent.dylib' (no such file), '/path/to/nonexistent.dylib' (no such file) (Fiddle::DLError)
from /Users/carlocab/.rbenv/versions/3.4.5/lib/ruby/3.4.0/fiddle.rb:93:in 'Class#new'
from /Users/carlocab/.rbenv/versions/3.4.5/lib/ruby/3.4.0/fiddle.rb:93:in 'Fiddle.dlopen'
from ./test.rb:4:in '<main>'
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Ok, thanks. Does the caller handle this case appropriately i.e. the exit code is as expected?
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| libproc = Fiddle.dlopen("/usr/lib/libproc.dylib") | ||
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| proc_pidpath = Fiddle::Function.new( |
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Suggested change
| proc_pidpath = Fiddle::Function.new( | |
| libproc_proc_pidpath_function = Fiddle::Function.new( |
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| pid = ARGV[0]&.to_i | ||
| exit 1 unless pid |
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Do this before anything else. Should produce an error message if there's no argument passed.
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| bufsize = 4 * 1024 # PROC_PIDPATHINFO_MAXSIZE = 4 * MAXPATHLEN | ||
| buf = "\0" * bufsize | ||
| ptr = Fiddle::Pointer.to_ptr(buf) | ||
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| ret = proc_pidpath.call(pid, ptr, bufsize) | ||
| puts ptr.to_s.strip if ret.positive? |
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Needs better comments here.
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| bufsize = 4 * 1024 # PROC_PIDPATHINFO_MAXSIZE = 4 * MAXPATHLEN | ||
| buf = "\0" * bufsize | ||
| ptr = Fiddle::Pointer.to_ptr(buf) | ||
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| ret = proc_pidpath.call(pid, ptr, bufsize) | ||
| puts ptr.to_s.strip if ret.positive? |
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Suggested change
| bufsize = 4 * 1024 # PROC_PIDPATHINFO_MAXSIZE = 4 * MAXPATHLEN | |
| buf = "\0" * bufsize | |
| ptr = Fiddle::Pointer.to_ptr(buf) | |
| ret = proc_pidpath.call(pid, ptr, bufsize) | |
| puts ptr.to_s.strip if ret.positive? | |
| buffer_size = 4 * 1024 # PROC_PIDPATHINFO_MAXSIZE = 4 * MAXPATHLEN | |
| null_buffer = "\0" * buffer_size | |
| pointer = Fiddle::Pointer.to_ptr(buffer) | |
| return_value = proc_pidpath.call(pid, pointer, buffer_size) | |
| puts pointer.to_s.strip if return_value.positive? |
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brew stylewith your changes locally?brew typecheckwith your changes locally?brew testswith your changes locally?HOMEBREW_FORCE_BREW_WRAPPERcan be used as a security/compliancefeature, but allowing it to be disabled by setting
HOMEBREW_NO_FORCE_BREW_WRAPPERleaves a pretty large hole in it thatallows it to be sidestepped.
Let's fix that by actually checking the path of the process that called
brew, and the verify that that path matches the configured value ofHOMEBREW_NO_FORCE_BREW_WRAPPER.